The use of silica as a filler is effective as a technique of achieving both reduction of the rolling resistance and enhancement of the braking performance on a wet road surface simultaneously. In this case, a silane coupling agent is necessarily used in combination with silica for ensuring further reduction of the loss and enhancement of the abrasion resistance. The silane coupling agent also has a function of preventing a vulcanization accelerator from being adsorbed on the silica surface through mutual action with the silica surface.
In the case where a silane coupling agent is used, however, an unreacted component may remain in rubber to cause rubber burning on kneading. Accordingly, it has been known that a small amount of a silane coupling agent is used in combination with a nonionic surfactant to provide a rubber composition that is excellent in low-loss property, wet performance, abrasion resistance, processability and the like without occurrence of rubber burning (see PTL 1).
In this case, however, the reaction between the silane coupling agent and silica may be inhibited due to the rapid adsorption of the nonionic surfactant to the silica surface. As a result, the reinforcement property of the silica and the rubber component may be reduced, and the rubber composition may be deteriorated in abrasion resistance.
PTL 2 proposes a rubber composition containing, as basic components, at least (i) one kind of a diene elastomer, (ii) a white filler as a reinforcing filler and (iii) an alkoxysilane polysulfide as a coupling agent (white filler/diene elastomer), along with (iv) an enamine and (v) a guanidine derivative.
PTL 3 discloses a rubber composition containing, as basic components, at least (i) one kind of a diene elastomer, (ii) a white filler as a reinforcing filler and (iii) an alkoxysilane polysulfide as a coupling agent (white filler/diene elastomer), along with (iv) zinc dithiophosphate and (v) a guanidine derivative.
PTL 4 describes a rubber composition containing at least (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and (iii) an alkoxysilane polysulfide (PSAS) as a coupling agent (inorganic filler/diene elastomer), as basic components, in combination with (iv) an aldimine (R—CH═N—R) and (v) a guanidine derivative.
PTL 5 proposes a rubber composition based on at least (i) a diene elastomer, (ii) an inorganic filler as a reinforcing filler and (iii) an alkoxysilane polysulfide as a coupling agent, associated with (iv) 1,2-dihydropyridine and (v) a guanidine derivative.
Examples where a silane coupling agent is enhanced in the activity of the coupling function thereof in consideration of the kneading condition include PTL 6.
However, these inventions are still not sufficient in the reaction between the silane coupling agent and the rubber composition, and there are room of improvement in the enhancement of the low-heat-generation property.